Use of map data converted in a computer processible form (hereafter referred to as ‘electronic map data’) has recently been spread to various fields. The electronic map data are used for display of maps on personal computers, navigation systems mounted on vehicles, display of maps via the Internet, and production of mechanicals for maps in print. Three-dimensional display is adopted in the navigation system to help the driver's intuitive understanding of the drive course. Three-dimensional display of building structures advantageously assists the user's easy specification of the current position and the drive course.
Three-dimensional data of the building structures are required for the three-dimensional display. Extensive labor is, however, required to obtain three-dimensional data, especially height-relating data, with regard to a large number of building structures as objects of display in the maps. Diverse techniques have been proposed to relive such enormous labor. Examples of the proposed techniques include a technique disclosed in Japanese Patent No. 3015353 and ‘Simulation in Automatic Measuring of Three-Dimensional Urban Space Data in Range Images’, Ghao Huijing et al. (Institute of Industrial Science, University of Tokyo), Vol. 36, No. 4, 1997, ‘Photogrammetry and Remote Sensing’, Japan Society of Photogrammetry and Remote Sensing. The former technique aims to relieve the load of data acquisition by ingeniously setting a measurement point of the height of a building structure and the direction of measurement. The latter technique acquires three-dimensional data by matching the results of ranging with a laser range finder with CCD images.
In order to attain three-dimensional modeling of a building structure with lack of three-dimensional data, the conventional method assumes a fixed height regardless of the actual height of the building structure, or estimates the height of the building structure by the number of stories. These methods, however, do not sufficiently reflect the actual state and only give pseudo three-dimensional modeling.
The conventional three-dimensional modeling method requires measurement of each building structure to effectuate modeling that sufficiently reflects the actual state. Three-dimensional modeling of a huge number of building structures is required to generate practical three-dimensional electronic map data. The above proposed techniques thus do not sufficiently relive the labor but still demand an extremely large amount of labor for generation of the three-dimensional electronic map data.
In the span of several years, some new building structures are constructed and some old building structures are demolished. In order to ensure the practical use of the three-dimensional electronic map data, three-dimensional modeling should be performed at intervals following such a change of the building structures. The conventional techniques, however, require a long time for three-dimensional modeling and thus do not meet this time-based demand.